1. Field of the Invention
The invention relates to the field of retaining devices adapted for securing sockets to the anvils of large pneumatic air guns.
2. Description of Prior Art
Retaining devices secure power driven sockets to the anvils of power drives. My two patents in this area consist of the Socket Retaining Ring, U.S. Pat. No. 4,266,453, issued in 1981 (the "1981 Patent"), and the Metal Shielded Retaining Ring, U.S. Pat. No. 4,583,430, issued in 1986 (the "1986 Patent").
Prior to the 1981 Patent, power driven sockets were secured to the anvil of a power drive using a metal pin inserted through the bores of the socket aligned with the through-hole of the anvil. To keep the pin in place, a rubber O-ring would be installed around the periphery of the socket, being fitted in an annular groove intersecting and covering the aligned bores.
The most dangerous aspect of this prior art was that workmen would often use the large impact tools by only inserting the pin without using the O-ring. Since the O-ring was separate from the pin, the O-ring could easily get lost, neglected or forgotten. Injury could occur during use when the metal pins were violently dislodged by centrifugal force as a result of a defective O-ring or the lack of the O-ring.
In addition, normal usage of the tool would cause wear and tear of the inner surface of the socket, causing the socket to fit less tightly onto the square end of the anvil. During operation, the worn-out socket would rotate relative to the anvil, creating a "scissors-like" action. This "scissors-like" movement applied a shearing force at two places between the inner surface of the socket and the anvil: 1) the first juxtaposition defined by the alignment of the first bore of the socket with the first end of the through-hole of the anvil; and 2) the second juxtaposition defined by the alignment of the second bore of the socket with the second end of the through-hole of the anvil. This shearing force occasionally caused the metal pin to be jammed in the bores of the socket, creating a major inconvenience as workers would have to drill out the lodged metal pins.
The 1981 patent sought to remedy these problems by making the O-ring and pin a single, integral piece made of elastomeric material. Being a single unit solved the problems caused by separate pieces. As a single unit, a worker could not use the pin without the O-ring, nor the O-ring without the pin. Furthermore, since the pin consisted of the same elastomeric material as the O-ring, workers no longer had to struggle with removing metal pins jammed at the bores of the socket.
However, rotational movement of the socket relative to the anvil would still occur as part of normal use. This rotational movement caused shearing of the elastomeric pin at the two juxtapositions.
The 1986 patent improved upon the 1981 patent by including a metal sleeve covering a portion of the elastomeric pin. The 1986 patent teaches placing a metal sleeve around the far end of the pin adjacent to the second juxtaposition, which is the juxtaposition furthest away from the base of the pin. Using the metal sleeve improved the safety of the completely polyurethane retaining device. However, since the metal sleeve was hollow, it could not withstand a strong shearing force. In such case, the shearing force could crush or shatter the metal sleeve, destroying the safety of the ring as well as making it very difficult to remove.
Furthermore, the metal sleeve in the 1986 patent covered only the portion of the pin adjacent to the second juxtaposition, leaving the portion of the elastomeric pin adjacent to the first juxtaposition without function. Since the elastomeric portion would be exposed to the shearing force after the failure of the metal sleeve, the shearing force would easily shear the elastomeric material at both juxtapositions, severing the pin from the O-ring and rendering the entire retaining device useless and unsafe.
Furthermore, both the 1981 and 1986 patents include a pin whose length is substantially close to the diameter of the O-ring itself. The long pin causes major difficulty for the user in insertion and removal. First, the long pin requires a user to pull a portion of the O-ring adjacent to the pin back far enough so that the tip of the long pin can enter the first bore of the socket. Second, the long pin requires the user to insert the pin all the way through so that it: 1) traverses the first bore of the socket to the first end of the through-hole of the anvil (i.e. the first juxtaposition), 2) traverses all the way across the through-hole of the anvil, and 3) exits the second end of the through-hole and enters the second bore of the socket (i.e. the second juxtaposition). Likewise, to remove the pin, the user would have to pull the O-ring back far enough so that the entire pin can exit the first bore from which it entered. The length of the pin makes insertion and removal inconvenient as the pin would have to traverse through both juxtapositions.
The prior art does not disclose a retaining device that can satisfactorily withstand the shearing force between the socket and anvil. Obviously, a ring that could withstand the shearing force would last longer and provide greater safety. Furthermore, the prior art teaches a retaining device that is inconvenient to insert and remove.
Therefore, what is needed is a retaining device that
1) will not be jammed, sheared or crushed upon normal usage; PA1 2) will be easier to insert and remove than the prior art; and PA1 3) will allow greater shear resistance with a larger solid steel insert that is substantially stronger and safer.